Zircon refractories



ZIRCQN REFRAQTQRIES Osgood J. Whittemore, 3n,

Norton Company, Massachusetts No Drawing. Application ()ctober 22, 19%,

Serial No. 464,187

4 Claims. (Cl. 106-57) Princeton, Mass, assignor to Worcester, Mass, :1eorperatinn of abandoned.

One object of the invention is to provide strong zircon refractories.Another object of the invention is to pro vide a superior compositionfor arc barriers in electrical circuit breakers. Another object is toprovide superior refractories for electrical insulating purposes,providing many advantages, i. e. rigidity coupled with strength, maximuminsulating properties coupled with high dielectric strength includingresistance to electrical breakdown, ready moldability so that intricateshapes can easily be made, coupled with the advantages of smallshrinkage during firing, inexpensiveness of the raw materials used tomake the refractories and relatively low temperature firing conditionsrequired.

Another object of the invention is to provide a superior refractoryporcelain for the spark plugs of internal combustion engines. Anotherobject is to provide zircon refractories for spark plugs that can befired at relatively low temperatures. Another object is to providerefractories especially adapted for high frequency electricalinsulation, as well as for use as radio and radar components. Anotherobject is to provide superior porcelains for coaxial cable terminals,for bushings, for transformers and for capacitor cases. Another objectis to provide an electrical porcelain for use at elevated temperatures.Another object is to provide an electrical porcelain for use atextremely high voltages. Another object is to provide an electricalporcelain having high thermal shock resistance.

Another object of the invention is to provide refractories of highthermal conductivity. Another object is to provide refractories of lowthermal expansion characteristics. Another object is to provideporcelains having very smooth surfaces. Another object is to provideporcelains having extremely high resistivity in the high megohm-cm.range especially at the lower temperatures. Another object is to providerefractories or porcelains of some or more of the characteristicsindicated having a long firing range. Another object is to providerefractories or porcelains having high resistance to abrasion. Anotherobject is to provide zircon refractories having some or all of thecharacteristics indicated which, during firing, have very littletendency to warp even in thin sections.

Other objects will be in part obvious or in part pointed outhereinafter.

The importance of porcelains in general for the manufacture ofelectrical insulating parts of various kinds probably needs no extendeddiscussion. Zircon porcelains have long been favored for such partsWhere high dielectric strength and resistance to electrical breakdownare important. While more expensive than silica, zircon of good grade isnot too expensive. But the manufacturers of zircon porcelains havehitherto encountered 2,746,874 Patented May 22, 1956 the difliculty ofexcessive shrinkage of zircon porcelains, causing a high percentage ofrejections and restricting the permissible shapes to simple ones. Iprovide a composition which undergoes relatively slight shrinkage infiring, or good strength in the fired pieces and which can be fired atreasonably low temperatures.

My composition ranges from to zircon, by weight. I can use commercialzircon having a purity of from 95 to 99% by weight zircon, ZrOz-SiO2. Inthe above statement any hafnia HfOz content is treated as zirconia,ZrOz, since this is commercial practice, the compounds of hafnium beingindistinguishable from the compounds of zirconium by ordinary chemicalanalysis and having the same physical properties and since all zirconiumcontaining ores contain a minor (but not insignificant) proportion ofthe element hafnium (in combined form).

I can use either granular or milled zircon or a mixture of the two inany proportions, the one or the other or the proportion being dependenton the fineness of structure or the strength required. For the finerstructures I use all milled or a high proportion of milled zircon; forthe stronger structures I use all granular or a high proportion ofgranular zircon. The granular zircon ranges from grit size No. 100 toNo. 280 while the milled zircon is 74 microns and finer.

The remainder of my composition is silicate bond and should analyzewithin the limits shown in the following table.

TABLE I Percentage by Oxlde Weight;

Lime, calcium oxide, OaO 23.3 to 48.2. Alumina, A1203 11.8 to 20.0.Silica, S102 39.2 to 62.2.

The silicate bond should have notmore than 10% of oxide material otherthan calcium oxide, alumina, silica and alkali oxide. I cannot avoidhaving less than .02% of alkali oxide and I prefer to keep the alkalioxide to .2% and below. However, I can tolerate up to 2.0% of alkalioxide. The silicate 'bond is practically all oxide, treating silicatesas oxides which is permissible, and the material other than oxidematerial in my composition will at the most be not more than 0.2%. Ifind it advantageous to have from 6% to 10% of the alkaline earth oxide,magnesium oxide otherwise known as magnesia, Mg'O, to depress themelting point of the bond which even without the magnesia has a fairlylow melting point due to so much of the alkaline earth lime, CaO. Forspark plug porcelains, for high frequency electrical insulation and forlike uses the alkali oxide content of the bond should be not greaterthan 0.2%, but for many other uses it can be up to 2.0%.

The alkali oxides present will of course be mainly soda and potash, NazOand K20 respectively. However, within the above limits the alkali oxidescan include the other three, lithia, rubidium oxide and cesium oxide.Whereas the alkaline earth oxides are not detrimental to the porcelainwith respect to the desired electrical properties, the alkali oxidessoda, potash and also those of less frequent occurrence lithia, rubidiumoxide and cesium oxide are detrimental to the porcelain, weakening itsdielectric strength, lowering its resistivity etc.

According to my present knowledge, for many practical purposes and(understanding that varying the amount of zircon will still permit themanufacture of many different porcelains) for the manufacture ofporcelains for many electrical uses I prefer a silicate bond analyzingabout as follows:

TABLE II Percentage Oxide by Weight Lime, calcium oxide, GaO I. 27Magnesia, MgO 6 Alumina, A1203 Silica, SiOz A} I can produce the bond ofTable II in many difierent ways, from many mixtures of clays andcompounds, but the following examples illustrate two convenient mixtureseach of which gives substantially the bond of Table II.

A typical analysis of Kentucky plastic fire clay which is a siliceousclay is as follows:

TABLE IV Percentage by weight Silica, SiOz 66.1 Alumina, A1203 21.3Titania, TiOz 2.6 Iron oxide, FezOa 1.0 Potash, K20 0.6 Soda, NazO 0.2Magnesia, MgO 0.1 Lime, CaO -1--- 0.0 Ignition loss 7.4 Example 11Ingredient treats Whiting, calcium carbonate. 37 Kentucky plastic fireclay... 48 Talc 15 As more specific examples of my invention I preparedmixtures as shown in the following table.

TABLE V Percentage of Ingredients by Weight GranularZh'con 90 50 90 5095 55 95 55 Milled Zireom- 40 40 40 40 Bondoi'ExampleI 10 10 5 5 Bond ofExample I 10 The above constitutes 10 examples of the invention. In noneof these examples was any attempt made to introduce any alkali oxide. IHowever, as impurity there was and there would be in each of theseexamples a very small amount of alkali oxide as impurity at least asmuch as .02%.

With each of these mixtures 1% of dextrine and from 1% to 2% of waterwere added and the resulting mix in each case was pressed into smallplates which were dried and fired at cone 12. I prefer that my zirconrefractories be fired at firing conditions at least as high as cone 8.All of the plates, after firing, were stronger than a composition of 50%granular zircon, 40% milled zircon, 9% clay and 1% talc fired at cone16. It thus appears that my composition makes stronger pieces when firedat relatively low temperatures than standard mixtures fired at cone 16temperatures. In general the higher the firing temperature the strongershould be the piece. The mixture of 50% granular zircon, 40% milledzircon and 10% of the bond of Example 11 was one of the best and theplates made therefrom were twice as strong as those made from 50%granular zircon, 40% milled zircon, 9% clay and 1% talc.

Articles of zircon refractories according to the present invention haveall the advantageous characteristics and features stated in the objects.It will thus be seen that there has been provided by this inventionzircon refractories in which the various objects hereinabove set forthtogether with many thoroughly practical advantages are successfullyachieved. As various possible embodiments may be made of the aboveinvention and as many changes might be made in the embodiment above setforth it is to be understood that all matter hereinbefore set forth isto be interpreted as illustrative and not in a limiting sense.

I claim:

1. Zircon refractories consisting essentially of from to zircon, theremainder silicate bond including and analyzing within the followinglimits:

Calcium oxide from 23.3% to 48.2% Alumina from 11.8% to 20.0% Silicafrom 39.2% to 62.2%

Alkali oxide from .0% to 2.0%

said silicate bond having not more than 10% of oxide material other thansaid calcium oxide, alumina, silica and alkali oxide and said silicatebond having not more than 0.2% of material other than oxide material,all percentages being by weight.

2.. Zircon refractories according to claim 1 in which there is at least6% of magnesium oxide, MgO.

3. Zircon refractories according to claim 2 in which the alkali oxidedoes not exceed .2%.

4. Zircon refractories according to claim 1 in which the alkali oxidedoes not exceed .2%.

References Cited in the file of this patent Riess: Clays (3rd ed.),1927, pp. 438-444.

1. ZIRCON REFRACTORIES CONSISTING ESSENTIALLY OF FROM 80% TO 95% ZIRCON, THE REMAINDER SILICATE BOND INCLUDING AND ANALYZING WITHIN THE FOLLOWING LIMITS: CALCIUM OXIDE FROM 23.3% TO 48.2% ALUMINA FROM 11.8% TO 20.0% SILICA FROM 39.2% TO 62.2% ALKALI OXIDE FROM .0% TO 2.0% SAID SILICATE BOND HAVING NOT MORE THAN 10% OF OXIDE MATERIAL OTHER THAN SAID CALCIUM OXIDE, ALUMINA, SILICA AND ALKALI OXIDE AND SAID SILICATE BOND HAVING NOT MORE THAN 0.2% OF MATERIAL OTHER THAN OXIDE MATERIAL, ALL PERCENTAGES BEING BY WEIGHT. 